1. Field of the Invention
The present invention relates to an anti-lock control method applicable to a vehicle which has a pair of left and right wheels connected together via a differential gear having a differential limiting function.
2. Description of the Prior Art
When rear wheels of a four wheel-drive vehicle or a rear wheel-drive vehicle, which wheels are coupled together via a differential gear, are subjected to anti-lock control operation, it is conventional to employ a system of controlling the braking forces to the rear wheels independently from each other or a low-select system permitting the braking forces to both the wheels to be reduced concurrently in response to a locking tendency appearing at one of the wheels which is rotating at a lower speed.
In case the left and right rear wheels are connected to each other via a differential gear having a differential limiting function, however, employment of the above anti-lock control systems would cause the following problems. That is, in the low-select system, when brake force is applied to both the left and right wheels which are travelling on road surfaces of different coefficients of friction, the tackiness of that wheel which is on the road surface having a higher coefficient of friction may be utilized only to a non-neglectably reduced extent, leading to lowering of the braking efficiency. This is particularly remarkable in a rear wheel-drive vehicle having a larger part of its load distribution placed on the rear wheels. On the other hand, the system applying anti-lock control to left and right wheels independently from each other requires two control channels, which is not desirable in respect of cost, weight and required space.